Many types of apparatus have been used in locational association with X-ray equipment, including those disclosed in the following U.S. patents:
U.S. Pat. No. 2,508,449 to C. P. Davis, Jr. et al, 5-23-50, shows apparatus that could be pivoted 180.degree. for vertical or for horizontal fluorescopic use;
U.S. Pat. No. 3,612,867 to N. Y. Rabodzei et al, 10-12-71, shows angle-adjustable X-ray/TV apparatus with tiltable reflection element;
U.S. Pat. No. 3,758,723 to D. T. Green et al, 9-11-73, shows an X-ray/TV system with angled mirror;
U.S. Pat. No. 4,233,516 to W. Trepte, 11-11-80, shows fluorescopic apparatus adjustable to horizontal and vertical positions.
As indicated, the purpose of the imager of the present invention is for taking x-ray images of a patient under treatment to make sure that the treatment region is correctly aligned with the x-ray field. The bi-directional imager was conceived while the present inventor was trying to design an x-ray imager which was to be attached to the rotating gantry of a radiotherapy x-ray machine. To cover the size of the x-ray images, the imager has to have a large fluorescence screen (about 50 by 50 cm) and a mirror of about the same size and these have to be arranged at a precise angle to each other. It is very difficult and very costly to build such an imager which is also retractable.
The retractability is very important. To take an image, the imager has to extend out and position opposite to the x-ray source behind the patient. If the imager does not retract from the extended position, it interferes with the technical setting up of the patient for treatment.
It occured to the inventor that, since a large portion of patient treatments are performed with the therapy machine pointing either in a horizontal position or pointing in vertically downward position, it would be more economical to build an imager that can image these two positions only. In that case, according to the present invention, it need not be attached to or supported by the rotating gantry, rather it can be on a movable cart. However, in order to make the imager bi-directional, the plane of the fluorescence screen with the associated mirror should be able to change direction readily and precisely from vertical to horizontal and vice versa. This is accomplished in this invention.
Among the principal objects and advantages are therefore to provide for the following.
Detection of geometric treatment errors:
Since, as noted, a large portion of patient treatments are performed with the x-ray pointing either vertically or horizontally, a guidance image can be obtained at the same time as the treatment, using principles of this imager. From the obtained position of the anatomic structures, it can be determined whether there is any misalignment of the x-ray field with respect to the target volume. If an error is detected, the patient setup can be adjusted correctly before the full radiation dosage is given.
In case treatment is not performed with the x-ray pointing in either of the two directions, vertically or horizontally, the patient can still be imaged in these two directions as "reference" position with a small dosage of x-rays. The patient can then be treated at other desired angles, but the reference images can be used in collaboration with similar images taken with other diagnostic machines (such as radiotherapy simulators, computed tomography scanners, etc.) which can image the patient in the two "reference" directions as well as in the treatment direction.
Documentation of treatment:
The images obtained by the imager can be recorded on magnetic storage media or optical storage media, and provides a permanent record of how the treatment was carried out.
Versatility in mechanical design:
The imager is relatively compact and easy and quick to position. It has only one imaging arm, but it can be rotated to image the patient with x-rays impinging in a selected one of two different directions (horizontal and vertically downward). It does not require two separate imaging arms, is well supported but lightweight, and convenient to use and can be fabricated at relatively low cost.
Simplicity:
Mechanically, the invention provides one rotating joint connecting two boxes together. The electro-optical components are few and simple to install and service.
In consonance with the above, ramifications of the invention can be said in other ways.
Correct patient setup for radiation therapy treatment relies on the reference anatomic landmarks. This imager can obtain image of such localization landmarks and convert it into electronic signals. By using a video digitizer, the image can be digitized into a computer in real-time. The image can then be enhanced to bring out low contrast objects using digital image processing technique. Thus, it facilitates the comparison of treatment position with the reference position of the patient. From this comparison, any error detected can be corrected before the full dose is delivered.
The video image can be stored in magnetic storage device or optical storage devices for documentation of treatments. It saves storage space compared with the conventional means of using photographic film.
From the brightness of the image and the time of irradiation, the dose delivered to the patient can be calculated. Thus provides an independent method to monitor the dose delivered to the patient.
The system can be extended to cover more angles if (1) in an embodiment the base of the lower box is made into a cylindrical sector and moves on a complementary circular track and (2) in another embodiment the screen can be tilted at a larger angle to the mirror as will be shown.